Reversible organic reaction reactions that were initiated by external stimuli contributed enormously to the field of sensor chemistry as both the reactant and product can be distinguished by specific optical, electrical properties. Being utilized in specific applications, the reaction initiation should require non-invasive and very cheap inputs. Though variety of chemical inputs such as heat, pH, light, electrical have been utilized, optical input has been a superior choice because of its spatial and temporal control. Azobenzene, diarylethylene and spiropyran chromophores have been utilized molecular switches triggered by light. Spiropyran is one of the photochromic compounds, it changed to blue color upon exciting with UV light and the reaction is reversible under visible or thermal conditions. The color produced by the formation of merocyanine. Spiropyran derivatives are most well-known as typical organic compounds which reversibly colors or decolorizes upon exposure to the energy of light or heat.
However, attempts to introduce conventional spiropyran derivatives into use encounters the problems like the colored form (or the colorless form) present in a solution or high polymer binder is low in stability to light or heat, the system immediately returns to colorless (colored). Also, when they repeatedly exposed to light and heat for coloration and decolorization (recording and erasure), the exposure to light gives rise to a side reaction, which decomposes or deteriorates the spiropyran derivative. Thus, the derivative is not fully resistant to repetitions. Although, the spiropyran derivative for use as a photochromic medium is usually dispersed in a high polymer substance, the derivative dissolves out from the high polymer substance, or separates out therefrom through phase separation since the derivative generally has low compatibility with the high polymer substance.
U.S. Pat. No. 5,252,742 disclosed a spiropyran compound represented by the formula (I)

wherein R1 is alkyl having 1 to 20 carbon atoms or aralkyl, R2, R3, R4 and R5 are the same or different and are each a hydrogen atom, alkyl having 1 to 6 carbon atoms, aryl or aralkyl, alkoxyl having 1 to 5 carbon atoms, halogen atom, cyano, trichloromethyl, trifluoromethyl or nitro, R6 and R7 are the same or different and are each a hydrogen atom, alkyl having 1 to 6 carbon atoms, aryl or aralkyl, halogen atom, cyano or nitro, X is an oxygen atom or sulfur atom, Y is Se or (CH3)2C<, Z is and X is a sulfur atom when Y is (CH3)2C<. The spiropyran compound of the present invention itself is usable as a material such as recording material, photosensitive material, optical filter or decorative material. The present compound can further be homopolymerized or copolymerized with other polymerizable compound into a high polymer spiropyran compound for application to optical devices or dynamic devices
Article titled “Spiropyrans as molecular optical switches” by B Seefeldt et al. published in Photochem. Photobiol. Sci., 2010, 9, pp 213-220 reports a water soluble switchable spiropyran derivative and demonstrates the first intermolecular single-molecule photoswitching experiments in polymers.
Chinese patent no. 101704921 disclosed a technique for preparing an ultraviolet discoloration acrylate polymers, in particular to the reaction of the spiropyran-based polymer having active spiropyran compound reactive with the acrylic polymer, wherein said spiropyran having the structural formula

Wherein the reactive group R may be a hydroxyl group or a carboxyl group.
The photochromic behavior of spiropyran in polymer matrices has been studied by several workers. It is known that the colour reversibility between the two forms is satisfactory only for a limited number of repetitive coloring and decoloring changes. Furthermore, the insertion of spiropyrans into polymer films decreases their photocoloration rate in comparison to that in liquid solutions.
Article titled “Photochromic Behavior of Spiropyran and Fulgide in Thin Films of Blends of PMMA and SBS” by J S Lin et al. published in Journal of Polymer Research, 2003, 10 (2), pp 105-110 reports two types of photochromic colorants of either spiropyran or fulgide were dispersed in thin films of blends of polymethyl methacrylate (PMMA) and styrene-butadiene-styrene copolymer (SBS) with various ratios. The thin films were illuminated with ultraviolet light (365 nm) under various temperatures. The results show that the color form of spiropyran is more stable in polar PMMA and caused a blue shift in the absorption spectrum of merocyanine.
Article titled “Photochromic behavior of spiropyran in polystyrene and polycaprolactone thin films—Effect of UV absorber and antioxidant compound” by A Samoladas et al. published in Dyes and Pigments, 2008, 76 (2), pp 386-393 reports the photochromic spiropyran 1′,3′-dihydro-8-methoxy-1′,3′,3′-trimethyl-6-nitrospiro[2H-1-benzopyran-2,2′-(2H)-indole] dispersed into polystyrene (PS) and polycaprolactone (PCL) matrices in the form of thin films. These photochromic films were illuminated with ultraviolet irradiation (365 nm) at room temperature and for different time periods in the absence and in the presence of a UV absorber and an antioxidant compound, at specific proportions. The polarity of the polymer matrix can induce the maximum absorbance of the photochromic compound. In pure polymers the most intense peaks occur at 608 nm in PS and at 589 nm in PCL.
Article titled “Photochromic behavior of spiropyran in polymer matrices” by Amir Tork et al. published in applied optics, 2001, 40 (8), pp 1180-1186 reports the photoexcitation, relaxation, and optical erasure regimes of spiropyran-(SP-) doped polymer films. Cellulose acetate, poly(vinyl acetate), and poly(methyl methacrylate) (PMMA) were used as host polymer matrices.
Article titled “Photo-responsive polymeric structures based on spiropyran” by L Florea et al. published in Macromolecular Materials and Engineering, 2012, 297 (12), pp 1148-1159 reports the review on incorporating polymeric materials into spiropyran units and focuses on the effectiveness of their reversible response to external photonic stimuli.
Article titled “Synthesis and Properties of Benzophenone-Spiropyran and Naphthalene-Spiropyran Conjugates” by M Tomasulo et al. published in J. Org. Chem., 2007, 72 (2), pp 595-605 reports four compounds integrating luminescent and photochromic components in their molecular skeletons. Two of them combine a nitrospiropyran photochrome with either one or two naphthalene fluorophores and can be prepared in three synthetic steps. The other two consist of a nitrospiropyran photochrome and a benzophenone phosphore connected by either ether or ester linkages and can be prepared in six or five, respectively, synthetic steps. The luminescent components of these assemblies are expected to transfer energy intramolecularly to the photochromic species upon excitation and encourage their photoisomerization.
Article titled “Photodynamic transport of metal ions” by J D Winkler et al. published in J. Am. Chem. Soc., 1989, 111 (2), pp 769-770 reports photodynamic ion transport using spiropyranindoline 3a and the chloride salts of zinc(II), copper(II), and cadmium(II). Changes in transport rate of an order of magnitude were observed.
Article titled “Synthesis and studies of photochromic properties of spirobenzopyran carboxy derivatives and their model compounds as potential markers” by A. V. Laptev et al. published in Russian Chemical Bulletin, 2014, 63 (9), pp 2026-2035 reports a number of photochromic markers, viz., spirobenzopyrans containing one or two active carboxy groups attached directly or through a spacer, as well as their model derivatives. The obtained compounds were characterized by instrumental methods of analysis. Spectrokinetic methods were used to study the behavior of the spirobenzopyran markers and the model derivatives in solutions in EtOH and toluene.
The main problem of spiropyrans is their low stability and for this reason several attempts have been performed in order to graft them in the backbone of a macromolecular chain or to incorporate them into a polymer matrix.